Ravna is very sure that the process of escaping from simulations must bottom out in finitely many steps. However there's a technique for implementing an infinite tower of simulations: an environment in which you can always break out of the current level of interpretation and get at the interpreter for that level, and go on digging indefinitely. More here.

Of course, there's still a base level -- the trick it uses is to create the interpretive levels only when they're entered. But even if you could somehow get out of the whole infinite tower, you still couldn't be sure that the level you found yourself at hadn't also just been created.